Optical waveguides are capable of being integrated on different kinds of substrates (e.g. glass, Gas, InP, Si) for the purpose of developing Optical Integrated Circuits (OICs). The optical waveguides can then be used to build integrated micro-devices such as attenuators, filters and multiplexers and to interconnect these devices on the same substrate. The multi-functionality achieved by the different devices in the optical chip allows for the development of advanced optical systems.
Several technological breakthroughs such as dense wavelength division multiplexing and optical amplification have allowed telecom networks to move towards operating fully within the optical layer where potential transmission speeds and capacity are greater. The operation of all-optical telecom networks (“Optical Networks”) is seen as the most viable answer to managing the exponential growth in demand for bandwidth in both an efficient and economical manner.
A primary technological barrier to fully functional Optical Networks is the need for all-optical switches. Optical Networks must employ reliable all-optical switching devices, which are able to avoid the traffic bottlenecks that result with electro-optical and opto-electrical conversions implemented in most systems today. In particular, optical space switching and optical wavelength switching, also known as optical wavelength conversion, are seen as two critical features for all-optical routing/switching devices in the developing Optical Networks. Moreover, the combination of all-optical space switching with all-optical wavelength switching is necessary for the development of all-optical non-blocking telecom subsystems.
In a prior art, the non-linear optical Kerr Effect has been implemented in a Non-linear Optical Loop Mirror (NOLM) by N. J. Doran and D. Woods (Optics Letters, Vol. 13, No. 1, January 1988). The NOLM consists of an optical fiber Sagnac interferometer. A first and intense incoming signal modulates the index of refraction of the optical fiber through the Kerr effect. A second counter-propagating or co-propagating optical wave, with a different wavelength, experiences a phase shift after one round trip around the loop. This phase shift depends on the intensity of the first optical wave since this intensity modulates the refractive index of the loop. As a result, the first optical wave can induce destructive or constructive interference of the second optical wave at the output of the interferometer. Thereby, the optical intensity modulation pattern can be transferred from the first optical carrier to the second optical carrier. This all-optical wavelength conversion has been demonstrated by transferring a square modulation pattern (representing digital data) from one optical carrier to another optical carrier. However, as the strength of the Kerr effect is quite weak in a glass optical fiber (˜3·10−20 m2/W, Govind P. Agrawal, Fibre-Optic Communication Systems, p. 62, second edition, Wiley-Interscience, 1997), the length of the optical loop must be very long (more than 10 km), rendering the technology of this prior art far too cumbersome for implementation in telecom or other industries requiring the use of micro-devices.
Semiconductor Optical Amplifiers (SOAs) have also been used to demonstrate wavelength conversion with a square modulation pattern (Optical Fiber Communications, Gerd Keiser, McGraw-Hill Companies, third edition, 2000, chapter 11). In this art, two SOAs are integrated in a Mach-Zender Interferometer (MZI), one SOA in each of the two arms of the MZI. The incoming optical carrier which has a wavelength λ1, the square modulation pattern of which has to be switched to a second optical carrier which has a wavelength λ2≠λ1, is coupled into the interferometer, is split between both arms of the MZI and propagates along them and through the SOAs. The second optical carrier, the optical intensity of which is continuous, is coupled into the MZI in the counter-propagating direction with respect to the incoming optical carrier, is split between both arms of the MZI and propagates along them and through the SOAs as well. Because of its intensity, the incoming signal modulates the refractive index of the SOAs by depleting more or less the carrier density in the amplifying medium. This modulates the phase of the second optical carrier as it propagates through both SOAs. At the output of the MZI, the two optical waves resulting from the split of the second optical wave interfere together constructively or destructively depending on the phase shift they experienced in the MZI arms. This phase shift is defined by the square modulation pattern of the incoming optical carrier. As a result, the optical intensity of the second optical carrier is modulated in intensity according to the square modulation pattern of the incoming optical carrier. The SOAs integrated in the MZI achieve thereby wavelength conversion. Although wavelength conversion is achieved, this technique suffers from sensitivity to light polarization and wavelength chirping in the amplifying medium and, therefore, limits conversion efficiency and bandwidth.